Combination ground and test switch apparatus for pressurized-gas-insulated high voltage systems

ABSTRACT

A combination ground and test switch apparatus for pressurizedgas-insulated high-voltage systems capable of selectively electrically grounding and/or testing through the use of a medium voltage electrical source selectively connectible to a system internal conductor which is completely surrounded by a grounded conductor and which is constantly maintained in a pressurized state.

United States Patent 1191 Graybill Apr. 8, 1975 [5 1 COMBINATION GROUNDAND TEST 3.567.885 3/1971 Boersma 200/148 R SWITCH APPARATUS FOR3.592.984 7/1971 Turgeon 200/148 R 3.665.135 5/1972 Boersma et a1200/148 F PRESSURIZEDGAS'INSULATED HIGH 3,778,574 12/1973 Clark 200/148B VOLTAGE SYSTEMS Inventor: Howard W. Graybill, G reensburg.

l-T-E lmperial Corporation, Spring House, Pa.

Filed: Mar. 12, 1974 Appl. No.: 450.466

Related U.S. Application Data Continuation of Ser. No. 280999. Aug. 16.1972.

Assignee:

Milliken 200/148 F Primary Eraminer-Robert S. Macon Attorney. Age/1!, orFirm-Ostrolenk, Faber, Gerb & Soffen [57] ABSTRACT A combination groundand test switch apparatus for pressurized-gas-insulated high-voltagesystems capable of selectively electrically grounding and/or testingthrough the use of a medium voltage electrical source selectivelyconnectible to a system internal conductor which is completelysurrounded by a grounded conductor and which is constantly maintained ina pressurized state.

7 Claims, 3 Drawing Figures COMBINATION GROUND AND TEST SWITC APPARATUSFOR PRESSURIZED-GAS-INSULATED HIGH VOLTAGE SYSTEMS This is acontinuation of application Ser. No. 280,999, filed 16 Aug. 1972.

The present invention relates to pressurized gasinsulated high-voltagesystems and more particularly to a novel combination ground and testswitch apparatus for testing high-voltage conductors completely enclosedin grounded metal covers without the need for either depressurizing orremoving the grounded covers.

BACKGROUND OF THE INVENTION In metal-enclosed pressurized-gas-insulatedhigh voltage switchgear, of the type described in US. Pat. Nos.3,546,356; 3,573,342; 3,643,003 and in pending application Ser. No.234,811, filed Mar. 15, 1972, now abandoned, all of which have beenassigned to the assignee of the present application, it is conventionalthat the high-voltage conductors be completely enclosed in groundedmetal housings or covers at all points along the system. The advantagesof this construction in both safety and reliability are obvious. Thereis, however, one decided disadvantage in that it is not convenient togain access to the enclosed high-voltage conductor for low-voltage testscommonly performed on a routine basis such as, for example, resistancetests on circuit breaker contacts, power-factor tests on transformerinsulation, and so forth.

Since it is desirable and even necessary to periodically measure thecontact resistance of circuit breakers by the application of a knownmeasured current across two terminals of the circuit breaker for thepurpose of measuring the voltagedrop between the terminals, it isconventional in outdoor substation design that this can be readilyaccomplished by clipping the test leads on to the exposed high-voltageconductors at the upper ends of their bushings. However, this is notpossible in metalenclosed pressurized systems since the high-voltageconductors are not exposed at any point along the system.

BRIEF DESCRIPTION OF THEINVENTION The present invention is characterizedby providing a combination ground and test switch apparatus forpressurized-gas-insulated high-voltage systems and the like whichmaintains the integrity of the pressurized system and which may beselectively operated to provide either grounding or voltage testingwithout the need for either depressurizing or removal of any of thesystem grounded housings or covers.

The present invention comprises a housing joined to the groundedenclosure of a pressurized-gas-insulated high-voltage system andhermetically sealed thereto with an opening provided in the aforesaidgrounded housing to provide communication between the interior of theswitchgear and the housing affixed thereto. A reciprocally movableswitch blade is mounted within said housing and is arranged to'be movedto a closed position within the interior of the switchgear equipment forengageme'ntwith a jaw structure which is surrounded by an electrostaticshield to reduce dielectric stresses within the switchgear. An operatingmechanism which may be safely manipulated from the exterior of thehousing is provided for moving the switch blade between its connectedand disconnected positions. The end of'the switch housing remote fromthe switchgear grounded housing is provided with a conductive terminalelectrically insulated from the test switch housing and is electricallycoupled to the movable blade by a flexible conductor which is providedso as to allow for free reciprocal movement of the switch blade withoutin any way affecting the integrity of the electrical connectiontherebetween. A conductive ground strap is normally coupled between theaforementioned terminal and the switchgear grounded housing to maintainthe conductive components of the switch housing at ground potentialduring intervals when no tests are being performed. To perform thedesired test, the conductive group strap is first removed and the switchblade is operated to the closed position to establish an electricalconnection between the aforementioned terminal and the central conductorof the switchgear network. A medium voltage source may then be coupledto the aforementioned terminal for test purposes without the need foreither depressurizing the switchgear equipment or removing any of itshousings or covers.

It is therefore one object of the present invention to provide a noveltest switch assembly and housing adapted for selectively and simplyperforming tests upon the internal high-voltage conductor ofmetalenclosed pressurized-gas-insulated high-voltage switchgear whileavoidingthe need for either depressurizing the switchgear network orremoving any of its housings or covers.

BRIEF DESCRIPTION OF THE FIGURES The above, as well as other objects ofthe present invention will become apparent when reading the accompanyingdescription and drawings in which:

FIG. 1 shows an elevational sectional view of a ground and test switchassembly embodying the principles of the present invention.

FIG. 2 shows a sectional view of the assembly of FIG. 1 looking in thedirection of arrows 2-2.

FIG. 3 shows a sectional view of the assembly of FIG. 1 looking in thedirection of arrows 3-3.

DETAILED DESCRIPTION OF THE FIGURES Copending application Ser. No.234,811 discloses a metal-enclosed pressurized-gas-insulatedhigh-voltage circuit breaker in which the high-voltage conductors arecompletely enclosed in grounded metal covers at all points. In equipmentof this type as well as other components of such a switchgear and/orpower distribution and transmission network it becomes desirable andeven necessary at periodic intervals to measure the contact resistanceof the circuit breakers as well as other components, by application of aknown measured current from one terminal of the breaker to the other inorder to measure the voltage drop between terminals. Since the centralconductors are metal-enclosed within conductive pressurized housings atall point, it is an object of the present invention to provide anassembly 10 of the type shown in FIGS. 13 to perform the necessary testprocedures without the need for depressurizing the system or removingany portion of the enclosure to gain access to the high voltageconductor. In pressurized gas systems of this type, it is furthernecessary to provide means for grounding the internal high-voltageconductor to provide complete safety for personnel at such times when itbecomes necessary to open the enclosure and gain access to internalpartsfor inspection, maintenance or repair. Grounding or earthingswitches, which establish a good metal connection between the internalconductor and the grounded metal enclosure are well known in the art.Such grounding switches must be capable of carrying the full groundfault current capability of the electrical system at the point ofconnection without being damaged or destroyed. The assembly of FIGS.1-3, which combines the functions of a grounding switch with those of atest switch, may be adapted for use in establishing an electricalconnection with an internal conductor 11 which is energized at a highvoltage in normal usage. The grounded metal enclosure 12 serves as themeans for retaining the pressurized insulating gas within the hollowspace 13 between the conductor 11 and the grounded enclosure 12.Suitable insulators or spacers formed of a solid material and describedin detail in US. Pat. No. 3,573,341, for example, act to maintainappropriate spacing and centering of conductor 11 relative to itsassociated grounded housing 12.

The test switch assembly 10, which may be selectively electricallyconnected with the switchgear highvoltage conductor 11, comprises ahollowsubstantially cylindrical shaped housing 14 secured by weldments14a and 14b to internal flanges 15 and 16, respectively. A disc-shapedmember 17 formed of a suitable insulating material such as phenolic orepoxy, forms the outer end of the ground and test switch housing and isjoined to internal flange 15 by fastening means 18 arranged at spacedintervals about the periphery of the disc. Synthetic resilient O-rings19 serve to seal and hermetically join disc 17 to the flange 15 of thehousing. Disc 17 is provided with a centrally located opening 17a forreceiving a copper terminal 20 which is preferably ccmented in place toprevent gas leakage. A fastening nut 21 threadedly engages the threadedportion of terminal 20 along the exterior of disc .17, while a fasteningnut 22 threadedly engages the opposite threaded portion of terminal 20for securing the end terminal 23a ofa flexible metallic conductor 23arranged in an undulating fashion, as can best be seen in FIG. 1. Theopposite end terminal 23b of flexible conductive cable 23 is secured toa clevis assembly 24 by fastening means 25,25. The clevis assembly issecured to the left-hand end of a switch blade 26 which is mounted forreciprocating action under control of a crank member 27 arranged topivot about an actuating shaft 7, which shaft is provided with apolygonal-shaped cross-section, as shown best in FIG. I, for. matingwith an opening 27a of similar shape provided within insulating crank27. Crank 27 is a bifurcated member having a pair of spaced parallelarms 27b and 270 (note especially FIG. 3) which arms are provided withsuitable openings for receiving a pin 28 secured between arms 27b and270 by cotter pins 29,29. The clevis assembly is provided with anelongated vertically aligned slot 24a adapted to slidably receive pin28. Bifurcated crank arm 27 is adapted to move between the solid linerepresentation of FIG. 1 to the dotted line representation 27. Duringsuch movement, pin 28 traverses an arcuate path represented by dottedline 28a. As a result of this movement, the clevis assembly 24 is movedfrom the solid line representation of FIG. 1, to the dotted linerepresentation 24' thereby causing switch blade 26 to move from thesolid line representation of FIG. 1 to the dotted line representation26, Due to the flexible characteristics of cable 23, the cable is freeto become elongated as shown by dotted line representation 23 in FIG. 1so as to freely permit the clevis assembly and switch blade to movetoward the engaged or connected position for test purposes, as will bemore fully described.

Internal flange 16 which forms part of the test equipment housing ismechanically and electrically joined to a cylindrical-shaped section 31joined to the switchgear grounded conductive housing 12 by a weldment,as shown at 32, and having a flange portion 31a joined to internalflange 16 by fastening members 33 arranged at spaced intervals aroundthe periphery of flange 31a. Flexible resilient synthetic O-rings 34provide for airtight joining between flanges 31a and 16 when fasteningmembers 33 are appropriately tightened.

An insulating guide bearing 35 has a flange portion 35a joined to theinner portion of flange 16 by fastening means 36 arranged at spacedintervals around flange portion 35a. Guide bearing 35 has a centralopening 35b whose interior surface is provided with a low friction liner37 which may, for example, be Teflon. Guide bearing 35 acts to guide themovement of switch blade 26 so as to prevent any movement thereoftransverse to the longitudinal axis 26a of switch blade 26. In additionthereto, a pair of guide rods 39 and 40 are mounted within the interiorof the test switch housing with their opposite ends being mounted withinsuitable diametrically opposed openings 15a-15b and 16a-l6b provided inflanges l5 and 16, respectively. Clevis assembly 24 is provided with twowing portions 24b and 24c each having an opening 24d and 24e,respectively, for slidably receiving guide rods 39 and 40 to guide thelinear movement of the clevis assembly and prevent any twisting movementthereof.

As shown best in FIGS. 1 and 2, the grounded conductive enclosure 12 isprovided with an opening 12a to facilitate the free reciprocatingmovement of switch blade 26. The hollow interior of the grounded testswitch housing is filled with an insulating gas maintained at the samepressure as the gas inside the main enclosure or housing 12. Guidebearing member 35 is provided with an opening 35b to permit thepressurized gas to move freely between the switchgear and test switchenclosures so as to maintain and equalize the pressure within the twoenclosures. The three major components of the housing, namely thecylindrical enclosure 14, disc member 17 and tube and flange mem-.

Under normal conditions, a conductive ground strap 39' is connectedbetween conductive terminal 20 and tube and flange member 31, as shownbest in FIG. 1. A first end of the strap is mechanically secured toterminal 20 by means of fastening nuts 40 and 41, while the opposite endthereof is coupled to flange portion 31a by fastening member 33'. In thearrangement shown in FIG. 1, it can be seen that the entire ground andtest switch assembly is maintained at ground potential, i.e., thepotential of grounded conductive housing 12. In order to ground theinternal conductor 1, shaft 7 is rotated in the direction shown by arrowA in FIG. 1 to move switch blade 26 into the dotted line position 26' soas to engage a tulip-type jaw contact assembly 42 comprised of aplurality of contact fingers 42a arranged at spaced intervals in aradial fashion and having spring members 42b urging the contact fingersinto engagement with tubular projection 11a secured to conductor 11 byfastening means 43 and to selectively engage the free end of switchblade 26 when it occupies the dotted line position 26. Conductive member44 comprises an electrostatic shield having a smooth exterior surfaceandan external radius of sufficient dimension so as to prevent thedevelopment of internal corona at the operating voltage and so as toreduce flashover voltage due to the concentration of dielectric stresswhich might otherwise occur at sharp points or edges on the high-voltageparts. The electrostatic shield '44 is provided with asuitable opening440 to permit the free reciprocating movement of switch blade 26.

in order to ground internal conductor 11, shaft 30 is rotated in thedirection shown by arrow A'of FIG. I to move switch blade 26 intoengagement with the contact assembly 42. When it is desired to connectany test device having a voltage of up to l0kV (relative to groundpotential) to the internal conductor, the grounding strap 39' is removedand the lead of the test device (not shown for purposes of simplicity)is connected to terminal by removing and reapplying the fastening nuts40 and 41. The bifurcated crank member 27, as was previously described,is formed of a suitable insulatingmaterial to permit movement of theswitch blade into and/or out of engagement with central high-voltageconductor 11 without endangering operating personnel.

It can be seen from the foregoing description that the present inventionprovides a novel grounding and test switch structure for use withmetal-enclosed pressurized-gas-insulated high-voltage switchgear and thelike wherein grounding of the internal high-voltage conductor andremoval of the ground therefrom may be simply and safely performedthrough the operation of an externally accessible operating mechanism.In addition thereto, the assembly facilitates the application ofhighcurrent medium voltage electrical sources to the internal conductorfor test and maintenance purposes without the need for eitherdepressurizing the switchgear network or removal of any housings orcovers.employed therein.

Although there has been described a preferred embodiment of this novelinvention, many variations and modifications will now be apparent tothose skilled in the art. Therefore, this invention is to be limited,not by the specific disclosure herein, but only by the appending claims.

What is claimed is:

1. For use in a metal-enclosed pressurized-gasinsulated high-voltageswitchgear system, a doublepurpose grounding and test switch assemblycapable of grounding a high-voltage internal conductor and of permittinga non-grounded electrical connection to the internal conductor for testpurposes, said assembly comprising:

a grounded conductive housing completely surrounding said internalconductor and having an opening provided therein;

a switch housing mechanically and electrically connected to saidgrounded conductive housing and having an opening at a first end thereofwhereby the pressurized interior of the grounded conductive housingcommunicates with the interior of said switch housing to maintain anequalized gas pressure therebetween;

a reciprocating conductive switch blade;

guide means mounted within saidswitch housing for guiding saidconductive switch blade to move along a substantially linear path andthrough the grounded conductive housing opening;

the internal conductor including a jaw blade structure;

drive means mounted within said switch housing for moving saidconductive switch blade from a first position whereby its free end isdisengaged from the jaw contact structure to a second position wherebythe free end of said conductive switch blade electrically engages thejaw structure;

a terminal mounted to the free end of said switch housing remote, fromthe grounded conductive housing and electrically insulated therefrom;

flexible conductive cable means positioned within said switch housingand electrically connected between said terminal and the end of saidconductive switch blade remote from the jaw structure for permittingfree reciprocating movement of said conductive switch blade whilemaintaining the integrity of a conductive electric path between saidterminal and said conductive switch blade;

said guide means including means for electrically insulating saidconductive switch blade from the grounded conductive housing and saidswitch housing;

said drive means including an actuating shaft having one end thereofextending outwardly from said switch housing to provide for movement ofsaid conductive switch blade from and to a position exterior of saidswitch housing; said terminal being selectively connected to groundpotential or to test equipment.

2. The device of claim 1 further comprising a conductive strapselectively connectible between said terminal and said switch housingfor maintaining said conductive switch blade at the voltage level ofsaid grounded conductive housing.

3. The device of claim 1 wherein said drive means further comprises acrank arm formed of an insulating material coupled to said operatingshaft for pivoting said crank arm about said operating shaft when saidshaft is rotated;

a clevis assembly coupled to the end of said conductive switch bladeremote from the internal conductor;

means for coupling the free end of said crank arm to said clevisassembly.

4. The apparatus of claim 3 wherein said drive means is furthercomprised of means for providing an airtight seal in the region wheresaid operating shaft protrudes from said switch housing to prevent theescape of the pressurized gas contained therein.

5. For use in a metal-enclosed pressurized gasinsulated high-voltageswitchgear system, a doublepurpose ground and test switch assemblycapable of grounding a high-voltage internal conductor and of permittinga non-grounded electrical connection to the internal conductor for testpurposes in which a grounded conductive housing surrounds the internalconductor and has an opening provided therein;

a switch housing mechanically and electrically connected to saidgrounded conductive housing and having an opening communicating with theopening of the grounded conductive housing whereby the pressurizedinterior of the grounded conductive housing communicates with thepressurized inte: rior of said switch housing to maintain an equalizedgas pressure therebetween;

a conductive switch blade;

drive means for moving said conductive switch blade from a firstposition whereby its free end is electrically disengaged from theinternal conductor to a second position whereby the free end of saidconductive switch blade electrically engages the internal conductor;

an electrical terminal mounted on said switch housing and electricallyinsulated from said switch housing;

conductive means positioned within said switch housing and electricallyconnected between said electrical terminal and said conductive switchblade and permitting free movement of. said conductive switch bladewhile maintaining the integrity of a conductive electric path betweensaid electrical terminal and said conductive switch blade;

said conductive switch blade being electrically insulated from saidgrounded conductive housing and said switch housing;.

a conductive strap selectively connectible between said electricalterminal and ground potential for maintaining said conductive switchblade at the voltage level of said grounded conductive housing when saidconductive strap is electrically connected to both said electricalterminal and ground potential;

said conductive strap designed to be removable to disconnect theelectrical connection between said electrical terminal and groundpotential to thereby permit a non-grounded electrical connection to bemade from test equipment to the internal conductor through saidelectrical terminal and said conductive switch blade without the need todepressurize the switchgear system and without the need to remove eithersaid switch housing or the grounded conductive housing.

6. The device of claim 5 wherein said switch housing and the groundedconductive housing are mechanically and electrically secured to eachother so that they are both maintained at the same ground potential.

7. The device of claim 6 wherein said drive means moves a portion ofsaid conductive switch blade through the opening of said switch housingand the opening of the grounded conductive housing to mechanically andelectrically engage the internal conduc- IOI'.

1. For use in a metal-enclosed pressurized-gas-insulated highvoltageswitchgear system, a double-purpose grounding and test switch assemblycapable of grounding a high-voltage internal conductor and of permittinga non-grounded electrical connection to the internal conductor for testpurposes, said assembly comprising: a grounded conductive housingcompletely surrounding said internal conductor and having an openingprovided therein; a switch housing mechanically and electricallyconnected to said grounded conductive housing and having an opening at afirst end thereof whereby the pressurized interior of the groundedconductive housing communicates with the interior of said switch housingto maintain an equalized gas pressure therebetween; a reciprocatingconductive switch blade; guide means mounted within said switch housingfor guiding said conductive switch blade to move along a substantiallylinear path and through the grounded conductive housing opening; theinternal conductor including a jaw blade structure; drive means mountedwithin said switch housing for moving said conductive switch blade froma first position whereby its free end is disengaged from the jaw contactstructure to a second position whereby the free end of said conductiveswitch blade electrically engages the jaw structure; a terminal mountedto the free end of said switch housing remote from the groundedconductive housing and electrically insulated therefrom; flexibleconductive cable means positioned within said switch housing andelectrically connected between said terminal and the end of saidconductive switch blade remote from the jaw structure for permittingfree reciprocating movement of said conductive switch blade whilemaintaining the integrity of a conductive electric path between saidterminal and said conductive switch blade; said guide means includingmeans for electrically insulating said conductive switch blade from thegrounded conductive housing and said switch housing; said drive meansincluding an actuating shaft having one end thereof extending outwardlyfrom said switch housing to provide for movement of said conductiveswitch blade from and to a position exterior of said switch housing;said terminal being selectively connected to ground potential or to testequipment.
 2. The device of claim 1 further comprising a conductivestrap selectively connectible between said terminal and said switchhousing for maintaining said conductive switch blade at the voltagelevel of said grounded conductive housing.
 3. The device of claim 1wherein said drive means further comprises a crank arm formed of aninsulating material coupled to said operating shaft for pivoting saidcrank arm about said operating shaft when said shaft is rotated; aclevis assembly coupled to the end of said conductive switch bladeremote from the internal conductor; means for coupling the free end ofsaid crank arm to said clevis assembly.
 4. The apparatus of claim 3wherein said drive means is further comprised of means for providing anairtight seal in the region where said operating shaft protrudes fromsaid switch housing to prevent the escape of the pressurized gascontained therein.
 5. For use in a metal-enclosed pressurizedgas-insulated high-voltage switchgear system, a double-purpose groundand test switch assembly capable of grounding a high-voltage internalconductor and of permitting a non-grounded electrical connection to theinternal conductor for test purposes in which a grounded conductivehousing surrounds the internal conductor and has an opening providedtherein; a switch housing mechanically and electrically connected tosaid grounded conductive housing and having an opening communicatingwith the opening of the grounded conductive housing whereby thepressurized interior of the grounded conductive housing communicateswith the pressurized interior of said switch housing to maintain anequalized gas pressure therebetween; a conductive switch blade; drivemeans for moving said conductive switch blade from a first positionwhereby its free end is electrically disengaged from the internalconductor to a second position whereby the free end of said conductiveswitch blade electrically engages the internal conductor; an electricalterminal mounted on said switch housing and electrically insulated fromsaid switch housing; conductive means positioned within said switchhousing and electrically connected between said electrical terminal andsaid conductive switch blade and permitting free movement of saidconductive switch blade while maintaining the integrity of a conductiveelectric path between said electrical terminal and said conductiveswitch blade; said conductive switch blade being electrically insulatedfrom said grounded conductive housing and said switch housing; aconductive strap selectively connectible between said electricalterminal and ground potential for maintaining said conductive switchblade at the voltage level of said grounded conductive housing when saidconductive strap is electrically connected to both said electricalterminal and ground potential; said conductive strap designed to beremovable to disconnect the electrical connection between saidelectrical terminal and ground potential to thereby permit anon-grounded electrical connection to be made from test equipment to theinternal conductor through said electrical terminal and said conductiveswitch blade without the need to depressurize the switchgear system andwithout the need to remove either said switch housing or the groundedconductive housing.
 6. The device of claim 5 wherein said switch housingand the grounded conductive housing are mechanically and electricallysecured to each other so that they are both maintained at the sameground potential.
 7. The device of claim 6 wherein said drive meansmoves a portion of said conductive switch blade through the opening ofsaid switch housing and the opening of the grounded conductive housingto mechanically and electrically engage the internal conductor.